Most earth moving operations, such as grading, scraping, tilling and plowing are performed with manual depth control, based on an operator's judgment and/or experience. Often, the operator's vision is obscured such that he cannot observe the depth of the working member to any degree of precision. Several sensing approaches have been suggested which employ transducers which are mounted such as to sense distance to the ground from a point above the ground. These are typically plagued with errors due to rubble, snow, ice or puddles of water on the ground surface. Also, vibrations imparted to the transducers affect their accuracy.